Hydraulic chain tensioner with directional vent device

Abstract

The present invention relates to a mechanism to prevent the incorrect assembly of an air vent disc in a hydraulic tensioner. The hydraulic tensioner includes a housing having a chamber. A hollow plunger is slidably positioned inside the chamber. The chamber contains a spring which biases the plunger in a protruding direction and an air vent disc provided inside the plunger. An air vent disc includes a first portion and a second portion. The first portion has a groove as a vent channel and a through-hole. The second portion has a central hole and a plurality of grooves extending radially and opening into the outer periphery of the vent disc. The outer diameter of the second portion is larger than the inner diameter of the aperture located at the upper end of the plunger tip.

What is claimed is:  
     
       1. A hydraulic chain tensioner comprising: 
       a housing having a bore;  
       a hollow plunger slidably received within said bore and forming a fluid chamber therebetween, said hollow plunger having an upper end, said upper end having an aperture, said aperture having an inner diameter;  
       a spring biasing said hollow plunger in a projecting direction from said bore; and  
       a vent including a disc having a periphery, a first portion and a second portion, said first portion having a first outer diameter and a surface with a vent channel formed therein, said vent channel having a first end terminating at said periphery of said disc and a second end terminating at a position to establish a first connection between the atmosphere and said fluid chamber through said aperture when said vent is assembled in said hydraulic chain tensioner with said first portion being adjacent said plunger upper end, said first connection permitting a first quantity of fluid flow therethrough;  
       said second portion being generally opposite said first portion, said second portion having an second outer diameter, said second outer diameter of said second portion being larger than said inner diameter of said aperture, said second portion having a vent bore extending in an axial direction of said second portion and at least one vent fluid passage extending from said vent bore and connecting said vent bore with an outer circumference of said second portion such that a second connection between the atmosphere and said fluid chamber is established when said vent is assembled in said hydraulic chain tensioner with said second portion being adjacent said hollow plunger upper end, said second connection permitting a second quantity of fluid flow therethrough, said second quantity being greater than said first quantity.  
     
     
       2. The hydraulic chain tensioner of  claim 1 , in which said periphery of said vent defines a clearance between said first portion of said vent and said hollow plunger. 
     
     
       3. The hydraulic chain tensioner of  claim 1 , wherein said periphery of said vent has a groove extending in said axial direction, said groove in communication with said first end of said vent channel to permit fluid flow from said fluid chamber to said first end of said vent channel. 
     
     
       4. The hydraulic chain tensioner of  claim 1 , wherein said vent channel has a circuitous path from said first end to said second end. 
     
     
       5. The hydraulic chain tensioner of  claim 4 , wherein said vent channel has a spiral shape. 
     
     
       6. The hydraulic chain tensioner of  claim 4 , wherein said vent channel includes a plurality of linear portions on said surface of said first portion of said vent, adjacent said linear portions of said vent channel being angled at least 90° with respect to each other. 
     
     
       7. The hydraulic chain tensioner of  claim 1 , wherein said vent fluid passage opening into said outer circumference of said second portion of said vent channel extends radially from said vent bore. 
     
     
       8. The hydraulic chain tensioner of  claim 7 , wherein said fluid passage is a groove formed on an end face of said second portion. 
     
     
       9. The hydraulic chain tensioner of  claim 1 , wherein said vent is biased by said spring against the inside of said upper end of said hollow plunger. 
     
     
       10. The hydraulic chain tensioner of  claim 9 , wherein said vent is constructed integrally with a pressure relief valve assembly, said pressure relief valve assembly being biased against the inside of said upper end of said hollow plunger by said spring, a through-hole being formed in the center of said first portion connected to said aperture and said vent bore to permit the flow of fluid from said pressure relief valve assembly to the atmosphere through the aperture. 
     
     
       11. The hydraulic chain tensioner of  claim 10 , wherein said second portion is inserted into an opening formed in an upper end of said pressure relief valve assembly. 
     
     
       12. The hydraulic chain tensioner of  claim 1 , further comprising a fluid passage formed in said housing to connect said chamber with an external source of pressurized fluid. 
     
     
       13. The hydraulic chain tensioner of  claim 12 , wherein a check valve is provided between said fluid chamber and said external source of pressurized fluid to permit fluid flow into said chamber while preventing flow in the reverse direction.